diff --git a/README.md b/README.md
index b7644d9..8be8aeb 100644
--- a/README.md
+++ b/README.md
@@ -18,8 +18,17 @@ android {
 
 ## Usage
 ```java
-String cmd = "ffmpeg -y -ss 1 -t 100 -accurate_seek -i " + videoPath + " -codec copy " + savePath;
-FFmpegInvoker.exec(cmd.split(" "), 100, new FFmpegInvoker.Callback() {
+// ffmpeg -y -ss 1 -t 100 -accurate_seek -i + videoPath + -codec copy + savePath
+// you can use FFmpegCmd to build an ffmpeg command
+FFmpegCmd cmd = new FFmpegCmd();
+cmd.append("-ss").append(1);
+cmd.append("-t").append(500);
+cmd.append("-accurate_seek");
+cmd.append("-i").append(videoPath2);
+cmd.append("-codec").append("copy");
+cmd.append(savePath);
+
+FFmpegInvoker.exec(cmd.build(), new FFmpegInvoker.Callback() {
     @Override
     public void onSuccess() {
 
@@ -31,7 +40,7 @@ FFmpegInvoker.exec(cmd.split(" "), 100, new FFmpegInvoker.Callback() {
     }
 
     @Override
-    public void onProgress(float progress) {
+    public void onProgress(float percent) {
 
     }
 });
diff --git a/app/src/main/java/com/github/xch168/ffmpeg/invoker/demo/FFmpegTestActivity.java b/app/src/main/java/com/github/xch168/ffmpeg/invoker/demo/FFmpegTestActivity.java
index 3e90590..40a7b95 100644
--- a/app/src/main/java/com/github/xch168/ffmpeg/invoker/demo/FFmpegTestActivity.java
+++ b/app/src/main/java/com/github/xch168/ffmpeg/invoker/demo/FFmpegTestActivity.java
@@ -1,17 +1,17 @@
 package com.github.xch168.ffmpeg.invoker.demo;
 
-import androidx.appcompat.app.AppCompatActivity;
-
 import android.app.ProgressDialog;
 import android.content.Context;
 import android.content.Intent;
 import android.os.Bundle;
 import android.os.Environment;
 import android.os.Looper;
-import android.util.Log;
 import android.view.View;
 import android.widget.Toast;
 
+import androidx.appcompat.app.AppCompatActivity;
+
+import com.github.xch168.ffmpeg.invoker.FFmpegCmd;
 import com.github.xch168.ffmpeg.invoker.FFmpegInvoker;
 
 import java.io.File;
@@ -86,15 +86,28 @@ public class FFmpegTestActivity extends AppCompatActivity {
     public void cutVideo(View view) {
         showProgress();
         String savePath = getSaveDir() + "out.mp4";
-        String cmd = "ffmpeg -y -ss 1 -t 500 -accurate_seek -i " + videoPath2 + " -codec copy " + savePath;
-        FFmpegInvoker.exec(cmd.split(" "), mCallback);
+        FFmpegCmd cmd = new FFmpegCmd();
+        cmd.append("-ss").append(1);
+        cmd.append("-t").append(500);
+        cmd.append("-accurate_seek");
+        cmd.append("-i").append(videoPath2);
+        cmd.append("-codec").append("copy");
+        cmd.append(savePath);
+
+//        String cmd = "ffmpeg -y -ss 1 -t 500 -accurate_seek -i " + videoPath2 + " -codec copy " + savePath;
+        FFmpegInvoker.exec(cmd.build(), mCallback);
     }
 
     public void extractFrame(View view) {
         showProgress();
         String savePath = getSaveDir() + "out.png";
-        String cmd = "ffmpeg -ss 10 -i " + videoPath + " -vframes 1 -y " + savePath;
-        FFmpegInvoker.exec(cmd.split(" "), mCallback);
+        FFmpegCmd cmd = new FFmpegCmd();
+        cmd.append("-ss").append(10);
+        cmd.append("-i").append(videoPath);
+        cmd.append("-vframes").append(1);
+        cmd.append(savePath);
+//        String cmd = "ffmpeg -ss 10 -i " + videoPath + " -vframes 1 -y " + savePath;
+        FFmpegInvoker.exec(cmd.build(), mCallback);
     }
 
     public static String getSaveDir() {
diff --git a/library/src/main/java/com/github/xch168/ffmpeg/invoker/FFmpegCmd.java b/library/src/main/java/com/github/xch168/ffmpeg/invoker/FFmpegCmd.java
new file mode 100644
index 0000000..b633fb0
--- /dev/null
+++ b/library/src/main/java/com/github/xch168/ffmpeg/invoker/FFmpegCmd.java
@@ -0,0 +1,34 @@
+package com.github.xch168.ffmpeg.invoker;
+
+/**
+ * Created by XuCanHui on 2020/4/1.
+ */
+public class FFmpegCmd {
+    private StringBuilder sb;
+
+    public FFmpegCmd() {
+        sb = new StringBuilder();
+        sb.append("ffmpeg");
+        append("-y");
+    }
+
+    public FFmpegCmd append(String param) {
+        sb.append(" ").append(param);
+        return this;
+    }
+
+    public FFmpegCmd append(long param) {
+        sb.append(" ").append(param);
+        return this;
+    }
+
+    public FFmpegCmd append(float param) {
+        sb.append(" ").append(param);
+        return this;
+    }
+
+    public String build() {
+        return sb.toString();
+    }
+
+}
diff --git a/library/src/main/java/com/github/xch168/ffmpeg/invoker/FFmpegInvoker.java b/library/src/main/java/com/github/xch168/ffmpeg/invoker/FFmpegInvoker.java
index 0e4180c..8376e62 100644
--- a/library/src/main/java/com/github/xch168/ffmpeg/invoker/FFmpegInvoker.java
+++ b/library/src/main/java/com/github/xch168/ffmpeg/invoker/FFmpegInvoker.java
@@ -22,16 +22,11 @@ public class FFmpegInvoker {
     public static native String getAVFormatInfo();
     public static native String getAVFilterInfo();
 
-    public static void exec(String[] cmds, Callback listener) {
+    public static void exec(String cmd, Callback listener) {
         sCallback = listener;
 
-        StringBuilder cmdBuilder = new StringBuilder();
-        for (String cmd : cmds)
-        {
-            cmdBuilder.append(" ").append(cmd);
-        }
-
-        Log.i(TAG, "ffmpeg cmd:" + cmdBuilder.toString());
+        String[] cmds = cmd.split(" ");
+        Log.i(TAG, "ffmpeg cmd:" + cmd);
 
         exec(cmds.length, cmds);
     }